Telephone system



June 17, 1941. F, ss 2,245,683

TELEPHONE SYSTEM Filed 001;. 2, 1939 8 Sheets-Sheet 1 ,/04 [O0 Manual P0817700 g D/sfcmf Line J/05 I06 J/07 Exchange Loa/ Exchange 5/22; Disfribufol a Link /50 Finder Stu.

INVENTOR Frank Kass/er ATTORNEYS June 17, 1941. KESSLER 2,245,683

TELEPHONE SYSTEM Filed Oct. 2, 1939 8 Sheets-Sheet 5 ATTORNEYS June 17, 1941. F KESSLER 2,245,683

TELEPHONE SYSTEM Filed Oct. 2, 1939 8 Sheets-Sheet 6 INVENTOR Frank Kass/er ATTORNEYS June 17, 1941. F. KESSLER TELEPHONE SYSTEM Filed Oct. 2, 1939 8 Sheets-Sheet 7 QON ta 953 $5 ATTORNEYS.

Patented June 17, 1941 2,245,683 TELEPHONE SYSTEM Frank Kcssler, Villa Park, Ill.,

ciated Electric Laboratories, Inc.,

assignor to Asso- Chicago, 111.,

a corporation of Delaware Application October 2, 1939, Serial No. 297,477

46 Claims.

The present invention relates to telephone systems and more particularly to testing apparatus for telephone systems of the automatic type.

An automatic telephone system conventionally comprises an exchange provided with a switch train, a number of subscriber substations and subscriber lines extending between the exchange and the subscriber substations. The switch train is under the control of substation equipment located at each subscriber substation and is operative to set up the various connections between the subscriber lines. Ordinarily the switch train is impulse responsive and the substation equipment located at each subscriber substation comprises a telephone instrument, a telephone switch and an impulse transmitter.

The operation of the switch train may be properly controlled from a subscriber substation only in the event the impulse transmitter thereat is operative to transmit impulses which have a speed within prescribed limits and which have a relationship between the make contact and the break contact thereof within prescribed limits. More particularly, the impulsing speed of the transmitter should be approximately ten impulses per second; while the relationship between the make contact and the break contact of each impulse should be approximately 40:60, the contacts being closed forty per cent and open sixty per cent of each impulse period. Moreover, the line conductors of the subscriber line must be free of ground and battery faults thereon and cross connection faults therebetween in order properly to control the operation of the switch train from the subscriber substation.

While'individual pieces of testing apparatus operative to test the impulsing speed of a transmitter, to test the impulse ratio of the make contact and the break contact of the impulses transmitted by a transmitter, and to test a subscriber line for the different types of faults thereon are usually provided in the exchange of an automattic telephone system, the different pieces of testing apparatus are ordinarily manually controlled at the exchange and require the services of a competent testman. Furthermore, it is ordinarily necessary to remove the transmitter from the subscriber substation to the exchange in order to perform the abovementioned tests thereon and to render out of service a subscriber line in order to perform the above-mentioned tests thereon.

Accordingly, it is an object of the present invention to provide in a telephone system of the type described, testing apparatus which is operative under the control of a subscriber substation to test both the impulse transmitter located at the subscriber substation and the subscriber line extending to the subscriber substation.

It is another object of the invention to provide in a telephone system of the type described, improved testing apparatus which is operative under the control of a subscriber substation to test the impulsing speed of the transmitter located at the subscriber substation.

Another object of the invention is to provide in a telephone system of the type described, improved testing apparatus which is operative under the control of a subscriber substation to test the impulsing speed of the transmitter lo-- cated at the subscriber substation.

Another object of the invention is to provide in a telephone system of the type described, testing apparatus which is operative under the control of a subscriber substation to test the impulse ratio of make contact to break contact of th impulsestransmitted by the transmitter located at the subscriber substation.

Another object of the invention is to provide in a telephone system of the type described. testing apparatus which is operative under the control of a subscriber substation to test a subscriber line extending to the subscriber substation.

It is a further object of the invention to provide composite testing apparatus operative under the control of a remotely disposed impulse transmitting device to test both the device and a line extending to the device.

A further object of the invention is to provide testing apparatus which is selectively operative to perform different tests upon an impulse transmitting device associated therewith and to perform different tests upon a line extending between the devlce and the testing apparatus.

A further object of the invention is to provide in a telephone system including a number of subscriber substations and an operator position, testing apparatus which may be selectively controlled from the subscriber substations and from the operator position.

A further object of the invention is to provide improved testing apparatus which is of sim:- ple connection and arrangement and which is economical to manufacture and thoroughly reliable in operation.

The features of the present invention are illustrated as being incorporated in an automatic telephone system comprising a distant exchang a local exchange including a switch train and a manual operator position, trunk lines extending between the distant exchange and terminating at the operator position, a number of subscriber substations, and'subscriber lines extending between the local exchange and the subscriber substations. Also, the local exchange comprises testing equipment accessible to the switch train and to the operator position.

In accordance with one feature of the invention the testing equipment comprises a test positioniincluding testing apparatus operative to test the impulse ratio of make contact to break contact of the impulses transmitted by an impulse transmitter associatedthi'ewith, a group of first testing units each operative to test the impulsing speed of an impulse transmitter associated therewith, and a group of second testing'units each operative to test for ground and battery faults on the line conductors and cross connection faults between the line conductors of a line associated therewith, the groups of first and second testing units being arranged in associated pairs.

In accordance with another feature of the invention the system comprises means controlled by initial operation of the substation equipment at one of the subscriber substations for associating the telephone instrument and the transmit ter thereat with the subscriber line extending between the subscriber substation and the local exchange and for associating the subscriber line with the switch train at the local exchange. Also the system comprises means controlled by a first initial operation of the transmitter for causing the switch train to select an idleone of the first testing units, means controlled by further operation of the transmitter for operating theone first testing unit, switching mean operative to associate the one first testing unit with the associated one of the second testing units, and means controlled by a second initial operation of the transmitter for causing the switch train to select an idle one of the second testing units. Further the system comprises means controlled by another operation of the substation equipment following the first initial operation and the further operation of the transmitter for. disassociating the transmitter and the telephone instrument from the subscriber line and for operating the switching means and for operating the one second testing unit, and means controlled by another operation of the substation equipment following the second initial operation of the transmitter for disassociating the transmitter and the telephone instrument from the subscriber line and for operating the second testing unit. Further the system comprises means controlled by further operation of the substation equipment for again associating the transmitter and the telephone instrument with the subscriber line.

In accordance with a further feature of the invention each of the first testing units is operative to transmit over the subscriber line to the subscriber substation a signal indicative of the tested speed of the transmitter, this signal comprising different numbers of splashes of tone; while each of the second testing units is operative to transmit over the subscriber line to the subscriber substation a signal indicative of a particular type of fault on the subscriber line in the event the subscriber line is tested as having a particular type of fault thereon, this signal comprising different numbers of splashesof tone.

In accordance with a further feature of the invention each of the first testing units comprises impulse responsive means operative to test the idle or busy condition oi the testing apparatus at the testing position, switching means operative to associate the first testing unit with the testing apparatus at the testing position in the event the testing apparatus at the testing position is tested idle, and means controlled when the first testing unit is associated with the testing apparatus at the testing position for rendering busy the testing apparatus at the testing position. The first testing unit and the testing apparatus at the testing position are so connected and arranged that the testing apparatus at the testing position is operated substantially simultaneously with the operation of the first testing unit in the event the switching means is Operated, The testing apparatus at the testing position and the first testing unit may be repeatedly operated in order to check the operation of the testing apparatus and the operation of the first testing unit by successively operating the impulse transmitter associated with the first testing unit to transmit successively a predetermined digit. Also the testing position comprises telephone apparatus and means operative to establish a connection vbetween the telephone apparatus and a telephone instrument associated with the first testing unit in the event the switching means is operated.

In accordance with a further feature of the invention the operator position comprises means for establishing a connection between the distant exchange and the local exchange, the connection including an impulse transmitting device at the distant exchange, and means for selecting an idle one of the first testing units and for associating therewith the established connection extending betweenvthe distant exchange and the local exchange, whereby the first testing unit may be operated by the impulse transmitting device in the distant exchange. Further the operator position comprises an impulse transmitter operative to cause operation of the impulse responsive testing means in the first testing unit,

whereby the testing appar'atus at the testing position may be associated with the first testing unit while the first testing unit is associated by way of the manual position with the established connection extending between the distant exchange and the local exchange, thereby to per-.

mit the impulse ratio of make contact, to break contact of impulses transmitted by the impulse transmitting device at the distant exchange to be tested by the testing apparatus at the testing position.

In accordance with a further feature of the invention, when an idle one of the first testing units is selected by the operator position the one first testing unit and the associated one of the second testing units are rendered busy to the switch train: when an idle one of the first testing units is selected by the switch train the one first testing unit is rendered busy to the switch train merits thereof, whereby the above-outlined and additional operating features are attained.

The novel features believed to be characteristic of the invention are set forth with particularity in the appended claims. The invention, both as to its organization and method of operation, together with further objects and advantages thereof will best be understood by reference to the following specification taken in connection withthe accompanying drawings in which Figures 1 to 8, inclusive, taken together, illustrate a telephone system having incorporated therein a testing system embodying the present invention.

Description of the apparatus incorporated in the telephone and testing systems.

to and terminating in an individual jack-J I05 at the manual position I04.

The local exchange II5 serves a number of local subscriber substations including the subscriber substation indicated at T and comprises an automatic switch train. The automatic switch train comprises a plurality of links including the link I50 and a distributor I00 for assigning idle ones of the links to the use of the subscriber substations. The link I50 comprises a finder portion or switch i5I which is preferaibly of the Strowger type and a selector portion or switch I52 which is preferably of the Strowger type. A subscriber line and a line circuit individual thereto are associated witheach subscriber substation, the subscriber line I20 and the line circuit I2I individual thereto being associatedwith the subscriber substation T.

Each of the finder switches has access to each of the subscriber lines, while each of the selector switches has access to a number of groups of connector switches, not shown, to a first group of trunks including the trunk I25 and to a second. group of trunks including the trunk I30.

Each of the subscriber substations is provided with a telephone instrument, a telephone switch. dialing apparatus and a ringer; while the manu- 9.] position I04 is provided with the usual telephone apparatus including a telephone instrument and a. number of cord circuits, one of the cord circuits being indicated at I05. Also, a second group of trunks including the trunk I 08 terminates in individual jacks at the manual position I04, the trunk I08 being terminated in anindividual jack 0 I01 at the manual position I04.

The testing system is disposed in the local exchange II5 and comprises a testing position 200, shown in Fig. 2,- and a plurality of testing apparatus, each testing apparatus including a dial testing unit and a line testing unit. Preferably, each testing apparatus is identical to the testing apparatus illustrated which comprises a dial testing unit 400, shown in Figs. 3, 4 and 5, and a line testing unit I00 shown in Figs. 6, 7 and 8.

Referring now to Fig. 2, the testing position of the dial testing units.

200 comprises conventional telephone apparatus MI, 9. meter 202 calibrated to measure the per cent make contact of an impulsing apparatus, an audible signal 201, a visual signal 206, a jack J2I0, two sets of control keys K220 and K230, a control trunk 240 and a control network connected and arranged in a manner more fully described hereinafter. v

Referring now to Figs. 3,4 and 5, the dial testing unit 400 comprises a switch S500 oi the minor type including two wipers EM and 503 provided with individually associated contact banks 502 and 504, a rotary magnet M505 for driving the wipers noted and a release magnet M506 for releasing the wipers noted and for causing the wipers to be returned to their normal positions. Also associated with the minor switch S500 is a set of switch springs S501 which is actuated into engagement when the wipers noted of the minor switch S500 are actuated away from their normal positions. Also, the dial testing unit 400 comprises a switch S5I0 of the rotary type including four wipers 5II, 5I3, 5I5 and 5I1 pro-' vided with individually associated contact banks 5I2,' 5I4, 5I 6 and 5I8, and a rotary magnet M5I9 for'driving the wipers noted. Also associated with the rotary switch S5I0 is a set of switch springs S5I3 which is actuated into engagement when the wipers noted of the rotary switch S5I0 are actuated away from their normal positions. Further, the dial testing unit 400 comprises a visual signal L508; a test key K565; a switching relay R3I0; an impulse relay R340; a hold relay R4I0; a battery reversing relay R450; 2. tone relay R530; three timing relays R560, R510 and R580; 'a number of control relays R300, R320, R330, R350, R360, R310, R380, R420, R430, R440, R460, R410, R520, R540 and R550; and a control network for the relays noted.

The dial testing unit further comprises apparatus operative to transfer a connection extending thereto from the manual position I04 by way of the trunk I08 or a connection extending thereto from the switch train by way of the trunk I25 to the control trimk 240 extending to the testing position 200, provided the control trunk 240 is not busy due to the previous transfer of a connection thereto by another one Also, the dial testing unit 400 comprises apparatus operative to transfer a connection extending thereto from the switch train by way of the trunk I 25m 2. transfer trunk 385 extending to'the associated line testing unit 100.

Referring now to Figs. 6, 'l and 8, the line testing unit 100 comprises test telephone apparatus 0 I4 including a telephone instrument; three fault imitation keys K882, K883 and K883; a hold relay R600; two timing relays ROI0 and R; an impulse relay R650; a battery reversing relay R120; a tone relay R880, 2. testing relay R840;

three test checking relays R110, R and R8I0;

a number of control relays R620, R630, R540, R660, R610, R1I0, R130, R135. R140, R160, R180,

' R800, R820, R830, R850, R850, R810 and R090;

and a control network for the relays noted.

It is noted that the trunk I 08 terminating at the manual position I04 is individual to the dial testing unit 400; the trunk I25 accessible to the switch train is individual to the dial testing unit 400; the trunk I30 accessible to the switch train is individual to the line testing unit 100; while the control trunk 240 extending to the testing position 200 is commonly associated with the dial testing units of the testing apparatus.

Before proceeding with the operation of the testing system in conjunction with the telephone system it is noted that the manual position I comprises apparatus operative to seize any one ofthe dial testing units by way of the associated trunk terminating at the manual position I and to establish a connection thereto from the distant exchange I by any one of the trunk lines terminating at the manual position I. The selector switch of each of the links in the switch train is selectively operative automatically to search for a trunk inthe first group of trunks extending to an idle one of the dial testing units and to search for a trunk in .the second group of trunks extending to an idle one of the'li e test-'- ing units, and to seize a trunk extending to an idle one of the units. Accordingly, the switch train may be selectively controlled to establish a connection from any one of the subscriber substations associated therewith to an idle one of the dial testing units and to establish a connection from any one of the subscriber substations associated therewith to an idle one -of the lin testing units.

Each of the dial testing units is operative to test by way of the switch train the dialing or impulsing speed of the dialing apparatus disposed at any one of the subscriber substations and to test by way of the manual position ill! the dialing or impulslng speed of any impulsing apparatus disposed in the distant exchange I00. Furthermore, after a connection has been established to any one of the dial testing units by way of the switch train or by way of the manual position I, it may be transferred by way of the associated control trunk to the testing position 2". in the event that the testing position 200 is idle at this time. Also, after a connection has been established to any one of the dial testing units by way of the switch train, it may be transferred by way of the associated transfer trunk totheassociated line testing unit.

Each of the line testing units is-operative to perform certain line tests upon any subscriber line in the system either when the connection is established to the line testing unit directly from the switch train or when the connection is transferred to the line testing unit from the associated dial testing unit. More particularly, each of the line testing units is operative to perform the following tests upon any subscriber line in-the system:

1. A test to determine whether there is a ground fault on either of the line conductors of the subscriber lines.';

2. A test to determine whether there is a cross connection fault between the line conductors of the subscriber line.

3. A test to determine whether there is a battery leak fault on either of the line conductors of the subscriber lines. 7

The apparatus at the testing position 2" is operative to test any connection transferred thereto from any one of the dial testing-units to determine the impulse ratio of the impulsing apparatus included in the connection. More particularly, the apparatus at the testing position Ill determines the per cent make contact of the impulsing apparatus included in the connection transferred thereto from one of the dial testing units.

speed and impulse ratio tests as well as complete line tests.

In order to control the testing system to perform an impulse speed test upon the impulsing apparatus in the distant exchange illl connected by way of one of the trunk lines to the manual position ill, a connection is first established from the manual position I" to an idle one of the dial testing units. The digit 0 is then dialed, thereby to cause the selected dial testing unit to perform the impulse speed test and thereafter transmit a characteristic tone over the connection indicative of the impulse speed of the impulsing apparatus in the distant exchange I". The digit 0 may be dialed several times in order to cause the selected dial testing unit to repeat the impulse speed test several times, thereby to check the operation of the selected dial testing unit.

In order to control the testing system to perform both an impulse ratio test and an impulse speed test upon the impulsing apparatus in the distant exchange I" connected by way of one of the trunk lines to the manual position I, a connection is first established from the manual position I to. an idle one of the dial testing units. Thereafter, the digit 2 is dialed at the manual position I in order to cause the selected dial testing unit to transfer the connection to the testing position 2", assuming that the testing position 200 is idle at this time. The impulsing apparatus in the distant exchange I" is then operated to transmit the digit 0 over the trunk line to the manual position iill, which digit it transmitted by way of the selected dial testing unit to the testing position 2", whereupon the meter 2'2 indicates the per cent makecontact of the impulsing apparatus in the distant I indicative of the impulse speed of the apparatus in the 'iiistant exchange Hi0 as previously explained.

In order to control the testing system to perform an impulse speed test upon the dialing apparatus at any one of the subscriber substations,

a connection is first established between the subscriber substation and one of the links in the -switch train. The digit I isthen dialed, thereby .to cause the selector switch of the selected link to search automatically for a trunk extending to an idle one of the dial testing units. After an idle dial testing unit has been found by the selector switch of the selected link in the switch train. the digit I is dialed at the dialing apparatus at the subscriber substation, whereupon the selected dial testing unit operates in order to perform the impulse speed test upon the dialing apparatus at. the subscriber substation and to return "over the connection a tone characteristic of the speed of the dialing apparatus at the subscriber substation as previously explained.

In order to control the testing system to perform both impulse ratio and impulse speed tests upon the dialing apparatus at any one of the subscriber substations, a connection is first established between the subscriber substation and one of the links in the switch train. The digit is then dialed, thereby to cause the selector switch of the selected link to search automaticalaccuses Iy for a trunk extending to an idle one of the dial testing units. After an idle dial testing unit has been found by the selector switch of the selected link in the switch train. the digits 2 and; are dialed successively, thereby to cause the previously described operations of the apparatus at the testing position 200 and the selected dial testing unit.

In order to control the testing system to perform a line test upon any one of the subscriber lines in conjunction with either an impulse speed test upon the dialing apparatus at the associated subscriber substation or an impulse speed by test and an impulse ratio test upon the dialing ap paratus at the associated subscriber substation, a connection is first establishedbetweeu'the subscriber substation 'andon'e ofthe links in the switch train as previously explained. After this connection has been established from the subscriber substation to one of the links in the switch train the digits and 0 or the digits 5, 2 and 0 are dialed at the dialing apparatus at the subscriber substation as previously explained, whereupon either the impulse speed test is performed by the selected dial testing unit or both the impulse ratio test and the impulse speed test are performed by the apparatus at the testing position 200 and by the selected dial testing unit as previously explained. "After the test or tests noted have been performed, the receiver of the telephone instrument at the subscriber substation is momentarily replaced upon itsassociated switchhook, thereby to cause the selected dial testing unit to operate and transfer the connection by way of the transfer trunk to the associated line testing unit. The line testing unit then operates to perform the line tests previously mentioned uponthe subscriber line. Subse- Operation of the testing system to test the impulse speed of the dialing apparatus at a subscriber substation In order to test the impulse speed of the dialing apparatus at one of the subscriber substations, such, forexample, as the dialing apparatus at the subscriber substation T, a call is first initiated at the subscriber substation upon the associated subscriber line. More particularly, the receiver of the telephone instrument at the subscriber substation T is removed from its associated switchhook, thereby to initiate a call upon the subscriber, line I20, whereupon the line circult-12L indiyi dually;associated with-the subscriber-line I20 operates to initiate operation of the distributor I60 included in the switch train by way of the control conductor C122. The distributor I00 by way of the trunk I24. The finder quently the receiver of the telephone instrument at the subscriber substation is removed from its associated switchhook, whereupon the line testing unit associated with the selected dial testing unit operates to cause a characteristic tone indicative of a particular type of fault to be returned over the connection in the event a fault is present upon the subscriber line.

In order to control the testing system to perform only a line test upon any of the subscriber lines, a connection is first established between the subscriber substation and one of the links in the switch train as previously explained. After this connection has been established from the subscriber substation to one of the links in the switch train, the digit 3 is dialed at the dialing apparatus at the subscriber substation as previously explained, whereupon the selector switch of the selected link in the switch train operates automatically to find a trunk extending to an idle one of the line testing units. After one of the line testing units has been found by the selector switch of the selected link in the switch train the receiver of the telephone instrument at the subscriber substation is momentarily replaced upon its associated switchhook, thereby to cause the selected line testing unit to perform.

the previously mentioned line tests upon the subscriber line. The receiver of the telephone instrument at the subscriber substation is then removed from its associated switchhook, whereupon the selected line testing unit operates to cause a characteristic tone indicative of a particular type of fault to be returned over the eonnection in the event a fault is present upon the subscriber line.

switch. III of the link I50 then operates to find the line I23, the line I23 extending to the line circuit I2 I and operatively connected to the subscriber line -I20. When a connection is thus established between the subscriber substation T and the finder switch I5I of the link I50, dial tone current is returned from the selector switch I52 of the link I50 over the subscriber line I20, thereby to indicate to the testman at the subscriber substation T that may proceed to dial the first digit. In the present instance, the testman at the subscriber substation T dials the digit 5, thereby to cause the selector switch I52 of the link I50 to operate automatically and search for a trunk in the first group of trunks extending to an idle one of the dial testing units.- Assuming that the dial testing unit 400 is the first idle dial testing unit In this group of units the selector switch I52 of the link I50 operates automatically to seize the trunk I25 individual to the dial testing unit 400 and included in the first group of trunks. The trunk I25 is marked for selection by the presence of battery potential upon the control conductor thereof. The path for applying battery potential to the control conductor CI23 of the trunk I25 extends from battery by way of the resistor 421, the contacts 435, C390, the contacts 520, C313, the contacts 303, C339 an: the contacts 333 to the control conductor CI 3.

This application of battery-potential to the control conductor CI23 of the trunk I25 causes the selector switch I52 to seize the trunk I25 and switch through, thereby to" establish a connection betwen the subscriber substation T and "the trunk I25. When the selector switch I52 switches through a loop circuit is completed for energizing in series the upper and lower windings of the impulse relay R340, this circuit extending from ground by way of the upper winding of R340, C331 and the contacts 308 to the line conductor CI2I of the trunk I25 and from battery by wayof the lower winding of R340, C330 and the contacts 303 to the line conductor CI26 of the trunk I25, the line conductors CI26 and CI2I of the trunk I 25 being connected together by way of the selector switch I52 and the finder switch I5I of thelink I50, the line I23, the line circuit I2I, the subscriber line I20 and the telephone instrument at the subscriber substation T.

When energized over the above-traced circuit the impulse relay R340 operates, to complete, at the contacts 342, a circuit for energizing the winding of the hold relay R4I-0, this circuit extending from ground by way of the resistor 420, the contacts 455, the ground conductor C351, the contacts 342, C350, the winding of R4", the

' battery conductor C350 and the contacts 451 to the ungrounded terminal of the grounded battery 420. when energized over the abovetraced circuit the hold relay R4I operates, to complete, at the contacts 3, a circuit for energizing the winding of the control relay R430, this circuit extending from the ground conductor C351 by way of the contacts 3 and the winding of R430 to the battery conductor C350. Also upon operating the hold relay R4I0 completes, at the contacts 4, a path for applying ground potential to the control conductor CI20 of the trunk I25, this path extending from ground by way of the contacts H I, C310, the contacts 303,

C330 and the contacts 308 to the control conductor CI20 of the trunk I25. Further, this path extends from the control conductor CI of the trunk I25 by way of the control conductor C300 of the transfer trunk 301 to the control conductor CI33 of the trunk I30. Accordingly, at this time direct ground potential is applied to the control conductors CI28 and CI33 of the respective trunks I25 and I30, thereby to mark these trunks as busy to the selector switches of the links having access thereto.

When energized over the above-traced circuit, the control relay R430 operatesto complete, at the contacts 436, an obvious circuit for energizing the winding of the control relay R440, thereby to cause the relay R440 to operate. Also upon operating the control relay R430 disconnects, at the contacts 433 and 434, the line conductors CH0 and GUI of the trunk I00 extending to the manual position I04 from the dial testing unit 400, thereby to prevent interference from the manual position I04. Also, the control relay R430 completes, at the contacts 43l, a circuit for illuminating the lamp L206 at the testing position 200, this circuit extending from ground by way of the contacts 43I, the conductor C245 of the control trunk 240 and the lamp L206 to battery. The illumination of the lamp L206 indicates to the operator at the testing position 200 that one of the dial testing units has been seized and that subsequently an impulse ratio test may be required. Further, the control relay R430 interrupts, at the contacts 435, the previously traced path for applying battery potential by wa of the resistor 421 to the control conductor CI28 of the trunk I25, ground potential being applied to the control conductor CI20 of the trunk I25 at this time as previously noted.

Upon operating, the control relay R440 completes, at the contacts 442, a path for applying ground potential to the control conductor- CI00 of the trunk I08 extending to the manual position I04, this path extending way of the contacts "I, C360, the contacts 442, C336 and the contacts 30l to the control conductor CI00 of the trunk I00. This application of ground potential to the control conductor CI00 of the trunk I00 marks this trunk as busy in the jack J I01 at the manual position I04. Also, the control relay R440 completes, at the contacts 446, a circuit for energizing the winding of the control relay R460, ground by way of the contacts 446 and 452 and the winding of R460 to battery. Further, the control relay R440 completes,

this circuit extending from 444, an obvious path for applying direct ground potential to the ground conductor C351 and completes, at the contacts 441, a circuit for energizing the lower winding of the tone relay R530, this circuit extending from the ground conductor C351 by way of the contacts 441, C410 and the lower winding of R530 to the battery conductor C350. When energized over the above-traced circuit, the tone relay R530 operates, to complete, at the contacts 53I, an obvious path for short-circuiting in series the upper and lower windings thereof. When the upper and lower windings of the tone relay R530 are thus shortcircuited, this relay restores, thereby to interrupt, at the contacts "I, the previously mentioned path for short-circuiting in series the upper and lower windings thereof, whereupon the previously traced circuit for energizing the lower windings thereof is recompleted. Accordingly, the tone relay R530 operates intermittently.

At this point it is noted that the principal relays in the dial testing unit 400 are operated and are held in their operated positions by way of circuits extending between the conductors C351 and C350. In the present instance ground potential appears upon the conductor C351, while battery potential appears upon the conductor C350. However, it is noted that under certain other conditions of operation, ground potential appears upon the conductor C350, while battery potential appears upon the conductor C351. More particularly, each odd time the dial testing unit 400 is seized foruse, ground potential appears upon the conductor C351 while battery potential appears upon the conductor C350. On the other hand, each even time the dial testing unit 400 is seized for use battery potential appears upon the conductor C351 while ground potential from ground byat the contacts appears upon the conductor 0350. This reversal of potential between the conductors C351 and C350 is efiected upon each alternate operation and restoration of the control relay R440 and 'is provided for the purpose of preventing the contacts included in the various circuits extending between the conductors C351 and- C300 from continuously conducting current in the same direction. Accordingly, this battery reversal arrangement between the conductors C351 and C350 prevents undue pitting and corrosion of the contacts included in the circuits extending between the conductors C351 and C350. The manner in which alternate operation and subsequent restoration of the control relay R440 effect the reversal of potential between the conductors C351 and C350 is explained below.

Upon the first operation of the control relay R440 the previously traced circuit for energizing the winding of the control relay R460 is completed, thereby to cause the relay R400 to operate. Upon operating, the control relay R400 prepares, at the contacts I, a holding circuit, traced hereinafter, for energizing the winding of the battery reversing relay R450. Also, upon operating, the control relay R400 prepares, at the contacts 402, an operating circuit, traced hereinafter, for energizing the winding of the battery reversing relay R450.

When the dial testing unit 400 is released the control relay R440 restores, to complete, at the contacts 445, the previously mentioned operating circuit for energizing the winding of the battery reversing relay R450, this circuit extending from ground by way of the contacts, 445, 402 and 450, and the winding of R450 to battery. when the winding of the battery reversing relay R450 is thus energized it operates, to complete, at the contacts 45!, the previously mentioned holding circuit .ior energizing the winding thereof, this circuit extending from ground by way of the contacts 45!, 440 and 45!, and the winding of R450 to battery. Also, upon operating, the battery reversing relay R450 completes, at the contacts 453, a holding circuit for energizing the winding the control relay R450, this circuit extending from ground by way of the contacts 445, 452. .453 and the winding of R450 to battery. Accordingly, at this time when the dial testing unit 400 is released, thebattery reversing relay R450 and the control relay R450 remain in their operated positions.

when the dial testing unit 400 is again seized for usethe control relay R440 reoperates in order to interrupt, at the contacts 445, the previously traced holding circuit for energizing the winding of the control relay R450, whereupon the relay R450 restores shortly thereafter, this relay being of the slow-to-release type. Upon reoperation the control relay R440 completes, at the contacts 445, an alternative holding circuit for energizing the winding of the battery reversing relay R450, this circuit extending from ground by way of the contacts 446 and 45! and the winding of R450 to battery. Accordingly, at this time the battery reversing relay R450 occupies its operated position while the control relay R450 occupies its restored position. Subsequently, when the dial testing unit 400 is again released, the control relay R440 again restores, to interrupt, at the contacts 445, the previouslytraced alternative holding circuit for energizing the winding of the battery reversing relay,R450, thereby to cause this relay to restore. Accordingly, at this time both the battery reversing relay R450 and the control relay R450 occupy their restored positions.

In view of the above description of operations of the control relays R440 and R450 and the battery reversing relay R450, it will be readily understood that each odd time the dial testing unit 400 is seized the battery reversing relay R450 occupies its restored position; and each even time the dial testing unit 400 is seized the battery reversing relay R450 occupies its operated position.

When the battery reversing relay R450 occupies its restored position, ground potential is applied by way of the previously traced path to the conductor C351 and battery potential is applied by way of the previously traced path to the conductor C359. On the other hand, when the battery reversing relay R450 occupies its operated position battery potential is applied to the conductor C351 and ground potential is applied to the conductor C359, the path for applying battery potential to the conductor C359 extending .from the ungrounded terminal of the grounded battery 429 by way of the contacts 455 to the conductor C351 and the path for applying ground potential to the conductor C359 extending from ground by way of the contacts 444 and 454 to the conductor C359.

Continuing now with the operation of the dial testing unit 400, ground potential appears upon the conductor C351 and battery potential appears upon the conductor C359 as previously explained and the tone relay R530 is operating intermittently. Each time the tone relay R530 operates a circuit is completed for charging the condensers 533 and 325 in series, this circuit extending from the ground conductor C351 by way of the contacts 441, C419, the contacts 53!, the condenser 533, C382, the contacts 413, C345, the contacts 354, the condenser 325, the contacts .332, 0331 and the contacts 308 to the line conductor C121 of the trunk I25, and from battery by way of the lower winding of the impulse relay R340, C330 and the contacts 305 to the line conductor CI25 of the trunk I25, the line conductors C125 and CI21 of the trunk |25 being connected togetherby way of the previously traced circuit including the receiver of thetelephone instrument at the subsm' iber substation '1. Each time the tone relay R530 restores, a path is completed for short-circuiting in series the condensers 533 and 325, this path extending from battery potential appearing upon the conductor C359 by way of the resistor 532, the condenser 533, a portion of the previously traced path, the condenser 325 and another portion of the previously traced path including the receiver of the telephone instrument at the subscriber substation T to battery potential at the lower winding of the impulse relay R340. Accordingly, each time the tone relay R530 operates and restores, the condensers 533 and 325 are charged and discharged, thereby to cause a tone to be reproduced in the receiver of the telephone instrument at the subscriber substation T.

When the testman at the subscriber substation T receives the dial tone he proceeds to dial the digit 0 at the dialing apparatus at the subscriber substation T. The dialing apparatus at the subscriber substation T operates in the usual manner, thereby intermittently to interrupt and to complete the previously traced circuit for energizing in series the lower and upper windings of the impulse relay R340; whereupon the impulse relay R340 intermittently restores and operates. Each time the impulse relay R340 restores, it interrupts, at the contacts 342, the previously traced circuit for energizing the winding of the hold relay R4l0 and each time the impulse relay R340 operates, it recompletes, at the contacts 342, the previously traced circuit for energizing the winding of the hold relay R4l0.- However, the hold relay R4|0 does not restore during impulsing, this relay being of the slow-to-release type. Also, each time the impulse relay R340 restores, it completes, at the contacts 343, a circuit for energizing the winding of the rotary magnet M505 of the minor switch S500, this circuit extending, when completed, from the ground conductor C351 by way of the contacts 343, C355, the contacts 4l4, C349 and the winding of the rotary magnet M505 to the battery-conductor C359. Each time the rotary magnet M505 of the minor switch S500 is energized, the rotarymagnet M505 operates to drive the wipers noted of the minor switch S500 one step in the clockwise direction away from their normal positions.

Upon the first restoration of the impulse relay R340 a circuit is completed for energizing the winding of the control relay R350, this circuit extending from the ground conductor C351 by way of the contacts 343, C355, the contacts 4,

C349, the contacts M2 and 313, C38l, the wiper 5H and engaged normal contact in the associated contact bank5 I 2 of the rotary switch S5 l 0, C389, the contacts 315 and the winding of R350 to the battery conductor C359. When energized over the above-traced circuit, the control relay R350 operates, to complete, at the contacts 354, an obvious circuit for energizing the winding of the control relay R350, thereby to cause the relay R350 to operate. Upon operating, the control relay R350 interrupts, at the contacts 354, the previously traced circuit for returning dial tone current over the subscriber line [20 and completes, at the contacts 30!, an obvious path in multiple with the contacts 4 for applying ground potential to the control conductors C [20 and CI of the respective trunks I25 and I00. Also, upon operating, the control relay.R350 interrupts, at the contacts 352, a circuit, traced hereinafter, for energizing the winding of the switching relay R3l0, thereby to prevent operation or the relay R3" at this time.

When the wipers noted of the minor switch S500 are rotated one step in the clockwise direction away from their normal positions the set of switch springs S501 is actuated into engagement, thereby to complete an obvious circuit for energizing the winding oi. the control relay R410 in order to cause the relay R410 to operate. Also, when the wiper 503 of the minor switch S500 is actuated away from its normal position one step in the clockwise direction into engagement with the first contact in the associated contact bank 504, a circuit is completed for energizing the winding of the control relay R310, this circuit extending from the ground conductor C351 by way of the contacts 343, C355, the contacts 4, C340, the contacts 353, C345, the wiper-J03- and engaged first contact in the associated contact bank 504 of the minor switch S500, C302 and the winding of R310 to the battery conductor C359. When energized over the above-traced circuit, the control relay R310 operates to complete, at the contacts 314, an obvious holding circuit ior energizing the winding of the control relay R350 and interrupts, at the contacts 312, a further point in a circuit, traced hereinafter,

between the dial testing unit 400 and the appa ratus at the testing position 200.

When the previously traced original circuit for energizing the winding of the control relay R350 is completed, at the contacts 343, incident to the restoration of the impulse relay R340, 2. multiple circuit is also completed for energizing the winding of the timing relay R510. This multiple circuit extends from the ground conductor C351 by way of the contacts 343, C355, the contacts 4, C349, the contacts 2 and 313, C3", the wiper 5| I and engaged normal contact in the associated contact bank 5l2 or the rotary switch S510, C389, the contacts 523, C505, the contacts 55! and the winding of R510 to thebattery conductor C350. When energized over the abovetraced circuit the timing relay R510 operates.

Upon operating, the timing relay R510 completes, at the contacts 5", an obvious circuit for energizing the winding of the timing relay R500, thereby to cause the relay R500 to operate. Upon operating, the timing relay R500 completes, at the contacts 58l, an obvious circuit for energizing the winding of the timing relay R550, thereby tocause the relay R560 to operate. Upon operating, the timing relay R550 interrupts, at the contacts 55!, the previously traced circuit for energizing the winding of the timing relay R510, thereby to cause the relay R510 to restore. Upon restoring, the timing relay R510 interrupts, at the contacts 51!, the previously mentioned circuit for energizing the winding of the timing relay R500, thereby to cause the timing relay R500 to restore and interrupt, at the contacts 50!, the previously mentioned circuit for energizing the winding of the timing relay R500. The timing relay R550 then restores, to recomplete, at the contacts 5, the previously traced circuit for energizing the winding 01 the timing relay R510, thereby to cause the relay R510 to reoperate. The timing relays R510, R500 and R500 continue to interact in the above-described manner. Each time the timing relay R510 operates it completes, at the contacts 013, an obvious circuit for onergizing the winding 0! the rotarymagnetlflll oi therotaryswitch B540; andeachtimethetiming relay R510 restores, it interrupts, at the contacts 510, the previously mentioned circuit for energizing the winding of the rotarymagnetlllll- Accordingly, the rotary magnet Hill of the rotary switch Sill operates intermittently. Each time the rotary magnet M5" operates, it conditions the wipers noted of the rotary switch Bill to be driven one step in the clockwise direction and each time the rotary magnet M5 restores, the wipers noted 01 the rotary switch are driven one step in the clockwise direction away from their positions.

Accordingly, at this time the wipers noted 01' the minor switch 8500 are being driven step by step in the clockwise direction due to the intermittent operation of the impulse relay R340; while the wipers noted or the rotary switch 85" are being driven step by step in the clockwise direction due to the interaction of the timing relays R550, R510 and R500.

when the wiper 5 of the rotary switch S5" is rotated one step in the clockwise direction and into engagement with the first contact in the associated contact bank 5l2, an alternative path is completed for applying ground potential to the conductor C505, this path extending from the ground conductor C351 by way of the contacts 352, C300, the wiper 5H and engaged first contact in the associated contact bank N2 of the rotary switch S5l0, C300 and the contacts 523 to the conductor C585.

From the foregoing description of the operations of the minor switch S500 and the rotary switch S5l0, it will be understood that the speed of operation of the wipers noted or the minor switch S500 corresponds to the speed of operation of the impulse relay R340,.which speed corresponds to the dialing speed of the dialing apparatus at the subscriber substation '1; while the speed of operation of the wipers noted 0! the rotary switch S5l0 corresponds to a standard speed as determined by the operations of the timing relays R550, R510 and R500. Accordingly, the wipers noted of the minor switch S500 and the wipers noted 01 the rotary switch S5l0 will engage the tenth contacts in the associated contact banks at substantially the same time in the event these switches are operated at the same speed. on the other hand, the wipers noted of the minor switch S500 will engage the tenth contacts in the associated contact banks before or after the wipers noted of the rotary switch S5" engage the tenth contacts in the associated contact banks in the event the minor switch S500 is operated respectively faster or slower than the rotary switch S5" corresponding to faster or slower than standard impulse speeds. The standard speed of the rotary switch 85", as determined by the timing relays R500, R510 and R500, is approximately ten or eleven steps per second corresponding to approximately ten impulses per second.

In the event the speed of the dial apparatus at the subscriber substation T is approximately ten impulses per second, the wiper 503 of the minor switch $500 will engage the tenth contact in the associated contact bank 504 at approxi- Bill, it-will be understood that in the event the mately the same'time the wiper oi the rotary switch S5l0 engages the tenth contact in the associated contact bank 5I3, whereupon a circuit is completed for energizing the winding of the control relay R540. The circuit for energizing the winding of the control relay R540 extends from the ground conductor C351 by way of the contacts 343, C355, the contacts 414, C349, the contacts 353, C345, the wiper 503 andensaged tacts 41I, 048i, the contacts 543 and the winding of R540 to the battery conductor C359.

In the eventthat the speed 01' the dialing appa ratus at the subscriber substation T is somewhat slower than ten impulses per second, the wiper 503 of the minor switch S500 will engage the tenth contact of the associated contact bank 504 of the minor switch $500 at approximately the same time the wiper 5" of the rotary switch S5|0 engages the eleventh contact in the associated contact bank 5l3, whereupon a circuit is completed for energizing the winding of the control relay R550. The circuit for energizing-the winding of the control relay R550 extends from the ground conductor C351 by way of the previously traced path to the wiper 503 and engaged tenth contact in the associated contact bank 504 of the minor switch S500 and therefrom by way of C595, the wiper 5l1, and engaged eleventh contact in the associated contact bank SW of the rotary switch S5l0, C594, the contacts SH and the winding of R550 to the battery conductor C359. When energized over the abovetraced circuit, the control relay R550 operates, to complete, at the contacts 553, a holding circuit for energizing the winding thereof, this circuit extending from the ground conductor C351 by way of the contacts 0411, C419, the contacts 41L C48l, the contacts 552 and the winding of R550 to the battery conductor C359. Also, upon operating, the control relay R550 completes, at the contacts 553, an alternative circuit for energizing the winding of the control relay R500, this circuit extending from the ground conductor C351 by way of the contacts 1, C419,- the contacts 411, C88l, the contacts 553 and the winding of R540 to the battery conductor C359. when energized over the above-traced circuit the control relay R540 operates, to complete, at the contacts 542, the previously traced holding circuit for energizing the winding thereof.

In the event that the speed of the dialing apparatus at the subscriber substation T is some- ,what faster than ten impulses per second, the

wiper 503 of the minor switch S500 will disengage the tenth contact in the associated contact bank impulsing speed oi the dialing apparatus at the subscriber substation 'I is approximately ten impulses per second only the control relay R540 is operated; in the event the impulsing speed of the dialing apparatus is somewhat slower than ten impulses per second, both of the control relays R545 and R550 are operated; and in the event the impulsing speed of the dialing apparatus is somewhat faster than ten impulses per second, neither of the control relays R540 and R550 is operated.

When the wiper 503 of the minor switch 8500 disengages the ninth contact in the associated contact bank, the previously traced circuit for energizing the winding of the control relayR310 is interrupted, thereby to cause the relay R310 to restore shortly thereafter, this relay being ofthe slow-to-release type. Upon restoring, the control relay R310 interrupts, at the contacts 314, the previously traced holding circuit for energizing the winding of the control relay R350,

' thereby to cause the relay R350 to restore shortly 505 before the wiper 5" of the rotary switch S5|0 engages the tenth contact in the associated contactbank 5l 8. Accordingly, in this event, neither of the control relays R540 or R550 is operated.

From the foregoing description of the operations of the control relays R540 and R550, as determined by the relative speed of operations of th minor switch S500 and the rotary switch thereafter, this relay being of the slow-to-release type. Upon restoring, the relay R350 interrupts, at the contacts 354, the previously mentioned circuit for energizing the winding of the control relay R350, thereby to cause the relay R350 to restore shortly thereafter, this relay being of the slow-torelease type. When the control relay R350 restores and prior to the restoration of the control relay R350, a circuit is completed for energizing the winding of the control relay R520, this circuit extending from the ground conductor C351 by way of the contacts 353, C335, the contacts 333 and 355, C344 and the winding of R520 to the battery conductor C359. When energized over the abovetraced circuit, the control relay R520 operates to complete, at the contacts 524, an obvious path for applying ground potential by way of the ground conductor C351 to the conductor C585, thereby to cause the timing relays R550, R510 and R580 to reoperate as'previously explained. The timing relays R550, R510 and R580 thenreoperate as previously explained, thereby in cause the rotary magnet M5I9 of the rotary switch S5l0 to be energized intermittently, whereupon the wipers noted of the rotary switch S5l0 are rotated step by step in the clockwise direction.

When the wiper 5|3 oi the rotary switch S5l0 is rotated to engage the first contact in the associated contact bank 5l'4,'a holding circuit is completed 'tor energizing the winding of the control relay R520, this circuit extending from the ground conductor C351 by way of the contacts 520, the wiperv 5|3 and engaged first contact in the associated contact bank 5l4 of the rotary switch S5|0,C533, the contacts 52 I, C354 and the winding of R520 to the battery conductor C359.- When the 'wlper 5" of the rotary switch 'S5I0 engages and subsequently disengages the'second contact in the associated contact bank 5&0, a splash of tone current is transmitted over the subscriber line I20 to the subscriber substation '1. More particularly, when the wiper 5l1 engages the second contact in the associated contact bank 5i0, a path is completed from the battery conductor C359 by way of the resistor 532, the condenser 533, C590, the wiper 5H and engaged second contact in the associated contact bank 5! of the rotary switch $5M, C595, the wiper 503 and engaged tenth contact in the associated contact bank 504 of the minor switch S500, C345, the contacts 354, the condenser 325, the contacts 332,

C331 andthe contacts 303 to the line conductor Cl21 of the trunk I25, battery potential being connected by way the lower winding 0! the impulse relay R3", Call and the contacts 800 to the line conductor CHI 01 the trunk Ill: and the line conductors Cl" and CR1 or the trunk "I being connected together by way 01 the loop circuit including the receiver of the telephone instrument at the subscriber substation T. Furthermore, a path substantially identical to that previously traced for transmitting an additional splash of tone current over the subscriber line I20 is completed when the wiper Ill engages the fourth contact in the associated contact bank I! oi the rotary switch Bill in the event the control relay RI occupies its operated position, this path extending from the battery conductor C3" by way of the resistor "2, the condenser I. the contacts 543 and I, CHI, the wiper I" and engaged fourth contact in the associated contact bank ill oi. the rotary switch Bill and C"! by way 0! the previously traced path including the receiver of the telephone instrument at the subscriber substation T to battery at the lower winding oi' the impulse relay R340. Finally, a path substantially identical to that previously traced for transmitting a further splash of tone current over the subscriber line I20 is completed when the wiper ill engages the sixth contact in the associated contact bank lit 0! the rotary 'switch S! III in the event both of the control relays R540 and R550 occupy their operated positions, this path extending from the battery conductor C359 by way of the resistor 532, the condenser 533, the contacts 543 and 554, G592, the wiper I" and engaged sixth contact in the associated contact bank 5l8 of the rotary switch Silll and C595 by way of the previously traced path including the receiver of the telephone instrument at the subscriber substation T to battery at the lower winding of the impulse relay R340. r

Accordingly, the operation of the rotary switch SSH? at this time is eflective to cause one splash, two splashes or, three splashes of toneicurrent to be transmitted over the subscriber line. I to the subscriber substation T in the event the'speed of the dialing apparatus thereat is respectively somewhat faster than ten impulses per second, approximately 'ten impulses per second, or somewhat slower than ten impulses 'per second. The number of. tone splashes which are received at the receiver of the telephone instrument at the subscriber substation'T is indicative of the speed of the dialing apparatus thereat. I

When the wipers noted of therotary switch SSH) are rotated back to their normal positions, the wiper SIB disengages the last contact in the associated contact bank 5 included in the previously traced holding circuit tor-energizing the winding-oi the control relay R520, thereby. to cause the relay R520 to restore. Upon restoring, the control relay R520 interrupts, at the contacts 524, the previously traced path for applying ground potential to the conductor C588, thereby to arrest further operation of the timing relays R560, R510 and R5, and consequently the rotary switch Sill.

Just prior to the operation oi the wipers noted mamas Slll, Clll, the contacts I and I2 and the winding 01 R42. to the battery conductor 08". when energised over the above-traced circuit.

, the control relay Rfll operates, to complete, at

of the rotary switch Sill back to their normal positions andwhen the wiper ll! engages the tenth contact in the associated contact bank ill, a circuit is completed for energizing the winding of the control relay R420, this,circuit extending from the ground conductor C351 by way of the contacts 353, C335, the contacts at and 3, C3, the wiper SIS, and engaged tenth contact in the associated contact bank ill 01 the rotary switch the contacts 622, a holding circuit ior energizing thewinding thereof, thiscircuitextendinghom the ground conductor C3" by way oi the contacts 1, Cl", C4", the contacts In and the winding 01' RI to the battery conductor CI". Also, upon operating, the control relay R420 completes, at. the contacts 423, a circuit for energizing the winding of the release magnet MI" 0! the minor switch Bill, this circuit extending from the ground conductor 08" by way or the contacts in, cm, the contacts 3 and "I, Clll, the wiper Ill and engaged tenth contact in the associated contact bank III or the rotary switch Sill, C4", the contacts All and 423,

C418, C411 and the winding of the release mag-' the winding of the control relay R". in order to cause the relay R410 to restore. Upon restoring, the control relay Rlll interrupts, at the contacts "I, the previously traced holding circuits tor energizing one or both of the control relays RI" and R5", thereby to cause the operated ones at these relays to restore.

At this time the apparatus in the dial testing unit I" occupies the same position it did after seizure of the dial testing unit llll and prior to .the time the digit 0 was dialed. Accordingly,

the digit 0 may be redialed one or more times at the dialling apparatus at the subscriber substation T in order to cause the dial testing apparatus I to operate one or more times and retest the impulse speed of the dialing apparatus at thesubscribersubstation T and thereafter transmit a tone characteristic of the speed of the dialing apparatus at the subscriber substation '1 over the subscriber line III to the receiver of the telephone instrument at the subscriber substation T. Hence, it will be understood that the dial testing unit "I may be repeatedly operated in order positively to check the impulse speed of the dialing apparatus at the subscriber substation T.

Before proceeding with the. description oi. the release of the apparatus in the dial testing unit "I, it will he assumed that it is desirable to test the impulse ratio of the dialing apparatus at the subscriber substation T as well as the dialing speed thereof alter the dial testing unit 400 has been seized.

Operation of the testing system to test both the impulse ratio and impulse speed of the dialingapparatus at a subscriber substation subscriber substation T,

.. enemas tion T and then dialing the digit has previously explained; Assuming that the link I50 is again utilized, when the dial testing unit 400 is seized by the selector switch I52 of the link I50, the relays R340, R4l0, R430, R440 and R460 operate as, previously explained.

The digit 2 is then dialed at the subscriber substation T, whereupon the relaysR350 and R360 are operated and the wipers noted of the minor switch S500 are operated away from their normal positions, thereby to cause the control relays R310 and R410 and the timing relays R560, R510 and R580 to operate as previously explained.

At this time the wipers noted of the minor switch S500 are operated into engagement with the. second contacts in the associated contactbanks. Moreparticularly, the wiper 50l engages the second contact in the associated contact bank 502 of the minor switch S500, thereby to com-. plete a circuit, traced hereinafter, for energizing the winding of the control relay R330; while the wiper 503 engages the second contact in the associated contact bank 504 of the minor switch S500, thereby to interrupt the previously traced holding circuit for energizing the winding of the control relay R310. Shortly thereafter, the control relay R310 restores in order to efiect the restoration of the control relays R350 and R360 Y in the associated contact bank 502 of the minor switch S500, C414, the contacts 42!, C361, the.

contacts 3H and the winding of R330 to the battery conductor C359.

When energized over the above-traced circuit, the control relay R330 operates, to interrupt, at

the contacts 332, the previously traced path for.

applying tone splashes which are normally produced incident to the reoperation of the rotary switch S5| 0 as determinned by the impulse speed test performed by the minor switch S500 and the rotary switch S5l0, as-previously explained. Also upon operating, the control relay R330 interrupts, at the contacts 333, the previously traced circuit for energizing the winding of the. control relay R520, thereby to prevent operation of the relay R520 at this time.

Upon restoring, the relay R350 interrupts, at the contacts 352, thepreviously traced path for applying ground potential to the conductor C585, thereby to arrest operation of the timing relays R560, R510 and R580." Also upon restoring, the control relay R350 completes, at the contacts 353, an alternative circuit for energizing the winding of the rotary magnet M5|9 of the rotary switch ssm, this circuit extending from the ground conductor C351 by way of the contacts 353, C335, the actor switch springs S5l9, C583, the wiper 5I3 and engaged contact in the associated contact bank 5l4 oi the rotary switch S5l0, the contacts 528 and 520, C566, the contacts 512, C581 and the winding of the rotary magnet M5l9 to the battery conductor C359. When energized over the above-traced circuit the rotary magnet M519 operates, to interrupt, at the contacts 520, the previously traced circuit for energizing the winding thereof, whereupon the rotary magnet M5I9 restores, to recomplete, at the contacts 520, the previously traced circuit for energizing the wind- 1 1 M5l9 operates intermittently, thereby to drive the wipers noted 01 the rotary switch S5l0 back into their normal positions, whereupon the wiper 6|3 disengages the last contact in the associated contact bank 5 connected to the conductor C583, thereby to interrupt the previously traced circuit for energizing the winding of the rotary magnet M5l9. Accordingly, at this time thewipers noted of the minor switch S500 engage the second contacts in the associated contact banks while the wipers noted of the rotary switch S5l0 engage the normal contacts in the associated contact banks.

Upon restoring, the control relayR360 completes, at the contacts 362', a test circuit for energizing the winding of the switching relay R3l0 in the event the testing position 200 is' idle at this time. Assuming that the testing position is idle at this time, the last-mentioned circuit extends from ground by way of the contacts 4, C318, the contacts 33l and 362, the winding of the relay R3l0, the contacts 3|8, C383, the chain circuit 323 extending through the other dial testing unit corresponding to the dial testing unit 400, C384, the contacts M9 and the resistor 324 to battery. Shortly after the switching relay R3l0 is energized over the above-traced circuit it operpoints in the previously mentioned circuit including the chain circuit 323, thereby to prevent operation of the switching relay in any of the other dial testing units corresponding to the dial testing unit 400 at this time in view of the fact that the testing position 200 is rendered busy by the operation of the switching relay R3l0.

Upon operating, the switching relay R3l0 completes, at the contacts 3i 1, a circuit for energizing the winding of the audible signal 201, this circuit extending from ground by way of the contacts 334 and 3| I, the conductor C244 01' the control trunk 240, the contacts 208 and the winding of the signal magnet 201 to battery. When energized over the above-traced circuit, the signal magnet 201 operates, thereby to interrupt, at the contacts 208, the previously traced circuit for energizing the winding thereof, whereupon the signal magnet 201 restores, to complete, at the' contacts 208, the previously traced circuit for energizing the winding thereof. Accordingly, the signal magnet 201 operates intermittently in order to produce an audible signal which indicates to the operator at the test position 200 that the control trunk 240 has been seized by one of the dial testing units and that an impulse ratio test is desired. 1

The operator at the testing position 200-then operates the control key K230 to its check position, thereby to complete a check circuit for the meter 202, this circuit extending from ground by way of the contacts 233 of the key K230, C234,

the resistor 204, the adjustable resistor 203 and the meter 202 to battery. The operator at the testing position 200 then adjusts the adjustable resistor 203 in order to cause the meter 202 to indicate one hundred per cent make contact. Thereafter, the key K230 is operated to its test position. When the key K230 is operated to its test position, it

ing thereof. Accordingly, the rotary magnet prepares, at the contacts 232,atest circuit, traced hereinafter, for energizing the meter 202 "in accordance with the per cent make contact of the dialing apparatus at the subscriber substation T and completes, at the contacts 2, a priming circuit for energizing the meter 202,the last-mentioned circuit extending from ground by way of the adjustable resistor 205, the contacts 23I of the key K230, the conductor C240 of the control trunk 240, the contacts In and 3, the conductor 0241 of the control trunk 240, the contacts 232 of the key K230, C234, the resistor 204, the adjustable resistor 203 and the meter 202 to battery. The-operator at the test position 200 then observes the meter 202 to determine whether or not the indication thereof corresponds approximately to the desired percentage make contact. This desired percentage make contact is approximately forty per cent, and in the event the indication of the meter 202 departs somewhat from the desired percent make contact, the resistor 205 is adjusted in order to cause the meter 202 to indicate the desired per cent make contact.

Also, upon operating, the switching relay R3I0 prepares, at the contacts 3" and 3l5,,a connection between the trunk I25 extending to the subscriber line I20 and the conductors C241 and C242 of the control trunk 240 extending to the control key K220 associated with the telephone apparatus 20I at the testing position 200. The operator at the testing position 200 then operates the key K220 to its start position, thereby to complete, at the contacts 224 thereof, acircuit for energizing the winding of the control relay R320, this circuit extending from ground by way of the contacts 224 of the key K220, the conductor C243 of the control trunk 240, the contacts3l6and thewinding ofR320to battery. When energized over the above-traced circuit, the relay R320v operates, to complete, at the contacts 32I, a circuit for energizing the winding of the release magnet M506 of the minor switch S5I0, this circuit extending from the ground conductor C351 by way of the contacts 32I, C356, the contacts 412, C416, C411 and the winding of the release magnet M506 to the battery conductor C359. When energized over the above-traced circuit, the release magnet M506 operates to release the wipers noted of the minor switch S500 and to cause these wipers to be returned to their normal positions; whereupon the set of switch springs S501 is actuated into disengagement, thereby to interrupt the previously mentioned circuit for energizing the winding of the control relay R410. The control relay R410 then restores, to interrupt, at the contacts 412, the previously traced circuit for energizing the winding of the release magnet M506. When the wiper 50I of the minor switch S500 is returned to its normal position, the previously traced circuit for 4 energizing the winding of the control relay R330 is interrupted, thereby to cause the relay R330 to restore. Upon restoring, the control relay R330 interrupts, at the contacts 334, the previously traced circuit for energizing the winding of the audible signal magnet 201 in order to arrest furvther operation thereof. Also the control relay the digit 0, thereby to cause the impulse relay R340 to operate intermittently as previously explained. The first timethe impulse relay R340 restores, it completes, at the contacts 343, the previously traced circuits for energizing the winding of the control relay R300 and the winding 01 the rotary magnet M005 of the minor switch 8500, thereby to initiate operation of the minor switch S500 and to cause the control relays R300, R300 and R310 to operate as previously ex- 'plained.

the key K230, C234, the resistor 204, the adjustable resistor 203 and the meter 202 to battery. The intermittent operation of the impulse relay R340 is eflective to complete intermittently the test circuit including the meter 202 previously traced, thereby to cause the meter 202 to produce an indication corresponding to the per cent operation of the impulse relay R340, and accordingly-the per cent make contact of the dialing apparatus at the subscriber substation T. The operator at the testing position 200 observes the indication of the meter 202 in order to determine whether the indication of the meter departs i'rom the desired per cent make contact indication thereof as determined bythe priming circuit previously traced.

The operation of the remainder of the apparatus embodied in the dial testing unit 400 and including the minor switch S500, the rotary switch S5I0, the timing relays R500, R510 and R580, and the control relays R420, R520, R540 and R550 is the same as that previously described. Accordingly, at this time the dial testing unit 400 effects the previously described impulse speed test upon the dialing apparatus at the subscriber substation T and subsequently causes tone splashes to be returned over the subscriber line I20 indicative of the speed of the dialing apparatus at the subscriber substation T in the manner previously described. As previously noted, the testman at the subscriber substation T may dial the digit 0 several times in order to cause the dial testing unit 400 to test several times the impulsing speed of the dialing apparatus thereat and to give the operator at the testing position 200 an opportunity to check several times the impulse ratio of the dialing apparatus thereat.

After the testman at the subscriber substation T has dialed the digit 0 one or more times and the impulse ratio tests and impulse speed tests have been performed several times, as previously described, the operator at the testing position 200 operates the key K220 to its talk position, thereby to complete, at the contacts 22I and 222, an operative connection between the/ telephone apparatus 20I at the testing position 200 and the telephone instrument at the subscriber substation T.

The above-mentioned connection extends from the line conductor CI20 of the trunk I25 by way of the contacts 306, C333, the contacts 3I5, the condenser 322, the conductor C2 of the control trunk 240, the contacts 22l of the key K220, the line conductor C220 of the line 225, the telephone apparatus 20I, the line conductor C221 of the line 225, the contact 222 of the key K220 and the conductor C242 of the control trunk 240, the contacts 3 and 312, C331, and the contacts 300 

